1. Field of the Invention
The present invention relates to an optical fiber and a method of manufacturing the same. The present invention can be applied to a 1.3-.mu.m single-mode ribbon fiber, a dispersion-shifted fiber, and a dispersion-compensated fiber, as well as any other types of optical fibers and their manufacturing methods, and is particularly suitable to a dispersion-compensated fiber having a high Ge content in its core, concretely, a dispersion-shift fiber(DSF) and a dipsersion-flat fiber(DFF) having a GeO.sub.2 content at about 0.5 to 1.0% in their cores, and a dispesion-compensation fiber(DCF) having a GeO.sub.2 content at about 1 to 3% in its core and a fiber for an optical amplifier and large PMD (Polarization Mode Dispersion: also called merely "polarization dispersion"), and a method of manufacturing the same.
2. Related Background Art
In a conventional optical fiber manufacturing method in which one end of an optical fiber preform is softened by heating and an optical fiber is drawn from it, it is difficult to make the core portion of the optical fiber and a cladding portion around the core portion to have perfectly circular and concentric sections, and the sections of the core portion and cladding portion usually become slightly elliptic or slightly distorted circular. Accordingly, the refractive index distribution in the sectional structure of the optical fiber is not completely uniform, which causes a difference in group velocity of two orthogonally polarized waves in the section of the optical fiber, thereby undesirably increasing polarization dispersion. For this reason, when the optical fiber is put into a practical use as a submarine cable or trunk cable that require large-capacity, long-distance transmission, the adverse influence of the polarization dispersion appears largely. Even in optical fibers having almost the same diameter, the higher the content of the dopant, e.g., GeO.sub.2, added to the core, the larger the polarization dispersion.